The most common means now employed to move power boats through the water is the longitudinally short screw propeller. The theory of the action of the screw propeller has been the subject of consideration by many investigators. One theory is that the propeller impresses change of motion upon the water without change of pressure except such as is caused by the rotation of the screw. Another theory is that the thrust is obtained by change of pressure, the only changes of motion being the circumferential velocity due to the rotation of the propeller. Still others are referred to as the momentum theory and the vortex theory. The confused nature of the water at the stern of a moving boat makes the application of theory to marine screw propeller operation extremely complicated and not definitively known. In any event, there is considerable slippage with the conventional screw propellers as between the distance advanced in the water compared to the linear feet of water actually passed through the propeller blades. Ideally the distance advanced should equal the number of linear feet of water passing through the blades from front to rear. The propeller in accordance with the present invention approaches that ideal.
The severe limitations of present and prior art screw type propellers mounted at the stern of the boat can be understood more clearly by observing the much greater propulsion force of large sea creatures such as dolphins and whales. Though weighing as much as many manufactured water vehicles, they generate enough propulsion force by movement of their tail fins, dorsal fins and other parts of their body to lift their substantial weight out of and above the surface of the water. No manufactured water vehicle having a conventional prior art propeller system is able to generate the propulsion force needed to accomplish that. By watching dolphins, whales and other huge water creatures and the much greater propulsion force they are able to generate by movement of their fins and other parts of their bodies, which is largely a semi-twisting and back-and-forth movement the thought arises as to how much greater propulsion force those sea creatures would be able to generate if they could rotate or spin their fins in a continuous ever increasing rotations per minute. If a quick half turn, or quarter turn of their elongated tail fin can generate enough propulsion force to lift those heavy sea creatures out of and above the water, think of how much greater propulsion force if those elongated tail fins could be continually rotated in continually increasing rotations per minute. Living sea creatures such as dolphins and whales cannot do that, but manufactured propeller systems having comparable elongated fins can be designed to simulate the natural motion of those large sea creatures and which can be continuously rotated in continually increasing rotations per minute. That concept is incorporated in the elongated spinning fin propellers in accordance with this invention, and in manufactured water vehicles having such spinning fin propellers installed thereon, resulting in greatly increased propulsion force of such propellers and such water vehicles through the water as well as increased velocity.
Another disadvantage of conventional screw propeller water craft is that large portions of the hull are in sliding-frictional contact with the water, requiring the propellers to push the hull head-on against the resistance of the water displaced with no means throughout such hull surface to assist in moving the craft forward. Ideally, all parts of a vehicle in frictional contact with a medium on which or in which it moves should either itself impart motion or else be converted from sliding friction to rotating or moving friction wherever possible. An automobile for example is in frictional contact with the ground at the four points where its wheels touch, the contacts being rotating or rolling friction and with two or more of the wheels under power to impart motion. If the two front wheels were held in fixed position or if the entire body of the car were in sliding frictional contact with the ground, and only the two rear wheels were imparting motion, this would be somewhat analogous in a land vehicle to the way conventional screw propeller boats are operated in the water medium. The frictional resistance of water is of course much less, but even here it would be of advantage to either convert sliding friction contact into rotating or moving friction or into actual motion imparting means. The propeller in accordance with the present invention accomplishes that objective in large part. Here again it is comparable to the movement of living water creatures who impart moving friction to the water throughout the entire portion of their bodies that is in contact with the water by their continuous back and forth movements. Rotational movement of a pair of elongated spinning fin propellers in accordance with this invention, mounted either adjacent to each other, or in longitudinal alignment, each rotated in opposite directions of rotation but with their elongated fins configured to propel them forward even though rotated in opposite directions of rotation, create comparable movement through the water for the entire length of the elongated propellers and of the hull of the boat adjacent to and above such elongated propellers.
The elongated propellers in accordance with this invention include one or more elongated blades which extend from the front end of the propeller to the rearward end in a slightly helical path that may be less than one full turn from the front end to the rearward end.
Conventional screw propeller water craft also encounter what is known as wave resistance, separate and apart from frictional resistance, thus incurring additional energy loss due to wave making. This particular resistance is not too considerable at low speeds but constitutes a greater portion of the total resistance at high speeds. It would be of advantage therefore to convert as much of the portion of a boat in contact with the water into means which would not make waves or which would reduce the size of the waves. The elongated propeller in accordance with the present invention accomplishes that objective. This is particularly true when two of such elongated spinning fin propellers, one with elongated blades extending in a right-hand-turn helical path and the other with elongated blades extending in the opposite left-hand-turn helical path, are mounted in side-by-side relationship and rotated in opposite directions of rotation which propels water downwardly between them as well as rearwardly, as disclosed in greater detail herein below and in the drawings. Such motion tends to not only propel a vessel forward, but to also lift it vertically in the water. When the elongated spinning fin propellers in accordance with this invention are mounted that way on a vessel, spaced apart longitudinal bars or skids may be secured to the vessel or propeller housing below the propellers along their entire length to rest on the bottom of the body of water in the event the vessel becomes grounded. The elongated propellers are thus held above the bottom of the body of water by such longitudinal bars and free to be rotated to exert lifting force by propelling water downwardly between the propellers as well as rearwardly, to thus free the vessel equipped with such propellers and spaced apart longitudinal bars or skids in accordance with this invention.